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Detection of Broad Hα Emission Lines in the Late-time Spectra of a Hydrogen-poor Superluminous Supernova

Yan, Lin and Quimby, R. and Ofek, E. and Gal-Yam, A. and Mazzali, P. and Perley, D. and Vreeswijk, P. and Leloudas, G. and De Cia, A. and Masci, F. and Cenko, S. B. and Cao, Y. and Kulkarni, S. R. and Nugent, P. E. and Rebbapragada, Umaa D. and Woźniak, P. R. and Yaron, O. (2015) Detection of Broad Hα Emission Lines in the Late-time Spectra of a Hydrogen-poor Superluminous Supernova. Astrophysical Journal, 814 (2). Art. No. 108. ISSN 0004-637X.

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Discovered by the intermediate Palomar Transient Factory (iPTF), iPTF13ehe is a hydrogen-poor superluminous supernova (SLSN) at z =0.3434, with properties similar to SN2007bi. The early observations show that iPTF13ehe rises within 83 - 148 days (rest-frame) to reach a peak bolometric luminosity of L^(peak)_(bol) ~1.3x10^(44) erg s^(-1), then decays very slowly at 0.015 magnitude per day. The measured ejecta velocity is ~13000km s^(-1). The inferred explosion characteristics, such as the ejecta mass (67 - 220M⊙), the total radiative and kinetic energy (E_(rad) ~10^(51) erg, E_(kin) ~2x10^(53) erg), is typical of SLSN-R events. However, the late-time spectrum taken at +251 days (rest, post-peak) reveals a Balmer Hα emission feature with broad and narrow components, which has never been detected before among other H-poor SLSNe. The broad component has a velocity width of ~4500km s^(-1) and has a ~300km s^(-1) blue-ward shift relative to the narrow component. We interpret this broad Hα emission line as the interaction between the supernova ejecta and a H-rich circumstellar medium (CSM) shell, located at a distance of ~4 x 10^(16) cm from the explosion site. This ejecta-CSM interaction can produce the observed Hα luminosity of ~2x10^(41) erg s^(-1) and causes the rest-frame r-band LC to brighten at late times. The fact that the late-time spectra are not completely absorbed by the shock ionized CSM shell implies that its Thomson scattering optical depth is likely ≤ 1, thus setting upper limits on the CSM mass ≤ 30M⊙ and the volume number density ≤ 4 x 10^8 cm ^(-3). The early-time spectra do not show any H emission lines from this CSM shell, indicating that most of the H-atoms are already neutral and the shell is optically thin to the visible light. We predict that this shell should produce Lyα absorption in the UV spectra. Of the existing models, a Pulsational Pair Instability Supernova (PPISN) model can naturally explain the observed 30M⊙ H-shell, ejected from a progenitor star with an initial mass of (95-150)M⊙ about 40 years ago. By searching the PTF database for events similar to iPTF13ehe, we estimate that about 10% of all SLSNe-I may have late-time Balmer emission lines from ejecta interactions with H-rich shells.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Yan, Lin0000-0003-1710-9339
Quimby, R.0000-0001-9171-5236
Ofek, E.0000-0002-6786-8774
Gal-Yam, A.0000-0002-3653-5598
Mazzali, P.0000-0001-6876-8284
Perley, D.0000-0001-8472-1996
Vreeswijk, P.0000-0002-7572-9088
Leloudas, G.0000-0002-8597-0756
De Cia, A.0000-0003-2082-1626
Masci, F.0000-0002-8532-9395
Cenko, S. B.0000-0003-1673-970X
Cao, Y.0000-0002-8036-8491
Kulkarni, S. R.0000-0001-5390-8563
Nugent, P. E.0000-0002-3389-0586
Rebbapragada, Umaa D.0000-0002-2560-3495
Woźniak, P. R.0000-0002-9919-3310
Yaron, O.0000-0002-0301-8017
Additional Information:© 2015 The American Astronomical Society. Received 2015 August 5; accepted 2015 October 13; published 2015 November 23. We thank the anonymous referee for the positive and constructive suggestions, which have helped to improve the paper. We benefited from discussions with Nick Scoville and Orly Gnat on collisional excitations in ISM. We thank Mansi Kasliwal, Thomas Prince, and Howard Bond for helping us obtain the P200 photometry at one epoch. Vicki Toy and John Capone from University of Maryland are acknowledged for taking the photometry observation using LMI on DCT. A.G.Y. is supported by EU/FP7 via ERC grant No. 307260, the Quantum universe I-Core program by the Israeli Committee for planning and budgeting and the ISF; by Minerva and ISF grants; by the Weizmann-UK "making connections" program; and by Kimmel and ARCHES awards. The Dark Cosmology Centre is funded by the Danish National Research Foundation. This paper made use of Lowell Observatory's Discovery Channel Telescope (DCT). Lowell operates the DCT in partnership with Boston University, Northern Arizona University, the University of Maryland, and the University of Toledo. Partial support of the DCT was provided by Discovery Communications. The Large Monolithic Imager (LMI) on DCT was built by Lowell Observatory using funds from the National Science Foundation (AST-1005313). LANL participation in iPTF is supported by the US Department of Energy as a part of the Laboratory Directed Research and Development program. A portion of this work was carried out at the Jet Propulsion Laboratory under a Research and Technology Development Grant, under contract with the National Aeronautics and Space Administration. US Government support is acknowledged. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: Palomar - , Keck - , SWIFT - , Discovery Channel Telescope - .
Group:Palomar Transient Factory, Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
European Research Council (ERC)307260
Israeli Committee for Planning and BudgetingUNSPECIFIED
Israel Science FoundationUNSPECIFIED
Danish National Research FoundationUNSPECIFIED
Discovery CommunicationsUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
JPL Research and Technology Development FundUNSPECIFIED
Subject Keywords:Stars: supernova, massive stars
Issue or Number:2
Record Number:CaltechAUTHORS:20150928-141615101
Persistent URL:
Official Citation:Lin Yan et al 2015 ApJ 814 108
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:60582
Deposited By: Tony Diaz
Deposited On:28 Sep 2015 23:42
Last Modified:21 Nov 2019 23:55

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